Re: [PATCH 11/11] kvm tools: Modify term_putc to write more than one char

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 06-05-2014 19:51, Andreas Herrmann wrote:

> From: David Daney <david.daney@cavium.com>

> It is a performance enhancement. When running in a simulator, each
> system call to write a character takes a lot of time.  Batching them
> up decreases the overhead (in the root kernel) of each virtio console
> write.

> Signed-off-by: David Daney <david.daney@cavium.com>
> Signed-off-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
> ---
>   tools/kvm/term.c |    7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)

> diff --git a/tools/kvm/term.c b/tools/kvm/term.c
> index 3de410b..b153eed 100644
> --- a/tools/kvm/term.c
> +++ b/tools/kvm/term.c
> @@ -52,11 +52,14 @@ int term_getc(struct kvm *kvm, int term)
>   int term_putc(char *addr, int cnt, int term)
>   {
>   	int ret;
> +	int num_remaining = cnt;
>
> -	while (cnt--) {
> -		ret = write(term_fds[term][TERM_FD_OUT], addr++, 1);
> +	while (num_remaining) {
> +		ret = write(term_fds[term][TERM_FD_OUT], addr, num_remaining);
>   		if (ret < 0)
>   			return 0;

    Perhaps 'return cnt - num_remaining' instead?

> +		num_remaining -= ret;
> +		addr += ret;
>   	}
>
>   	return cnt;

WBR, Sergei